As an emergency switch mechanism for stopping a robot in emergency, there is known what is called a deadman switch mechanism. Usually, the deadman switch mechanism is provided at one place or a plurality of places on a teaching operation panel connected to a robot controller. In normal operation, an operator holds the teaching operation panel and operates the robot while applying an external operation force (pressing, gripping, etc.) to an external operation force applicator (lever, button, knob, handle, etc.) of the deadman switch.
Most conventional deadman switches use a two-position type switch mechanism. Specifically, the two-position type deadman switch mechanism is an enable/disable switch mechanism having two positions of an applicator position at which the robot motion is disabled and an applicator position at which the robot motion is allowed. FIGS. 15a and 15b show an outline of a two-position type switch mechanism used for a conventional deadman switch; FIG. 15a shows a state in which an external operation force is not applied, and FIG. 15b shows a state in which an external operation force is applied.
Referring to FIGS. 15a and 15b , for the external operation force applicator of the deadman switch mechanism, a main lever L1 provided exposedly on a operation surface of a teaching operation panel and an ancillary lever L2 pushed by a plunger PL provided to the main lever L1 are pivotally supported by an axis AX1 with an elastic biasing force S1 indicated by the arrow mark.
When starting the robot operation, the operator pushes down the main lever L1 from the OFF state shown in FIG. 15a with a force overcoming the elastic biasing force S1. Accordingly, the ancillary lever L2 is pushed down and a movable contact element ME provided on a contact mechanism section CM is moved to the ON position, so that the ON state shown in FIG. 15b is established. In this ON state, the robot motion is permitted. The movable contact element ME normally has the OFF position; it is biased toward the OFF position (position projecting upward) by a publicly known proper biasing mechanism (not shown) and a stopper mechanism.
If an emergency stop of robot becomes necessary during the operation of robot, the pushing pressure of the main lever L1 is released from the ON state shown in FIG. 15b . Then, the main and ancillary levers L1 and L2 are returned to a neutral position (or a position regulated by a stopper) by the elastic biasing force S1, so that the state shown in FIG. 15a is established. In this state, the robot motion is prohibited.
When the operator feels a necessity for the emergency stop of robot, he/she must stop the application of external operation force of the deadman switch mechanism by an action such that his/her finger is set free from the lever (operation external applicator) or such that his/her hold of the teaching operation panel itself is released.
However, considering the operator's psychology, such an action can not always be taken reflectively when a state of emergency is created. In particular, the action such that the operator's hold of the teaching operation panel is released is accompanied by a psychological resistance, which delays the emergency stop of robot, whereby there may be a possibility of bringing about a dangerous situation.
For this reason, in addition to the conventional two-position switch mechanism of OFF (external operation force is not applied; robot motion is prohibited) and ON (external operation force is applied; robot motion is permitted), there has been proposed a three-position switch mechanism of OFF (external operation force is not applied; robot motion is prohibited), ON (external operation force is applied; robot motion is permitted), and OFF (external operation force is applied; robot motion is prohibited) such that the robot can be stopped in emergency by pressing a switch button with an especially strong force.
However, the conventionally proposed three-position deadman switch mechanism has disadvantages that the mechanism is large and complex and that it is difficult to apply an external force so that two states, a state in which the robot motion is prohibited and a state in which the robot motion is permitted, are distinguished definitely from each other while the external operation force is applied.